The incidence and severity of pertussis have been controlled by widespread immunization with DTP which contains inactivated Bordetella pertussis organisms (cellular vaccine). The identification of pertussis toxin, an extracellular protein of this pathogen, as a major, if not the sole protective antigen, was the basis for producing a new vaccine with improved safety and immunogenicity characteristics. B. pertussis was cultivated in a 100L fermenter and the pertussis toxin extracted from the culture supernant by affinity chromatography. The pertussis toxin was inactivated by hydrogen peroxide treatment under controlled conditions. The resultant toxoid, NICHD-PTxD, had less than 1% of its original binding and enzymatic activities by in vitro assays. In vivo assays, which require binding and enzymatic activity on the same molecule, showed no residual activity. Based upon the clinical satisfactory and serologic response in adults injected with this toxoid, two clinical studies with this pertussis toxoid have been completed in 18 month old children. The first, in Boston, gave one injection into 18 month old children previously immunized during infancy with the recommended three doses of DTP. The second gave two, and in some cases three injections, of this toxoid in Swedish children without previous history of either pertussis or known DTP vaccination. The results of both studies show that the pertussis toxoid has both superior safety and immunogenicity characteristics compared to the cellular vaccine component of DTP. The new batch of pertussis toxoid has been formulated and clinical testing of this material for safety immunogenicity in infants and, hopefully, effectiveness in that age group is planned.